Fig 4. Resulting forces at the position of the second right and third left teeth over the functional range of the mandibles.

A) F _act, i.e. forces generated by the faster muscle fibres (for details see text). B) F _tot, i.e. total bite forces including tonic and passive contributions. C) Residual forces at the position of the second right and third left teeth over the functional range of the mandibles. Residual forces represent the sum of passive joint forces and tonic contributions while their effective contributions depend on the opening angle. Forces were determined for the instances directly prior to a contraction and are consequently restricted to medium and large opening angles. In B and C, the red lines show the mean (solid), ± standard error (s.e.m.; dashed) and ± standard deviation (s.d.; dotted) of the passive forces, i.e. those forces necessary to open the mandibles of freshly killed specimens. At small and medium opening angles, the residual forces (F _res) are primarily generated by tonic muscle fibres while at high opening angles passive forces dominate.